In the production of electronic components such as largescale integrated circuits (LSI), microprocessing techniques using photolithography have been employed. In these techniques, a resist solution is first applied to a substrate to form a resist film. Then, the obtained resist film is exposed to a light pattern or a scanning beam, and developed with an alkali solution or other developer to form a resist pattern. Next, the exposed substrate is etched by RIE or other method, with the resist pattern used as a mask, to draw fine lines and spaces. Then, finally, the resist is removed.
Therefore, a resist for this purpose generally should be highly resistant to dry etching.
For this reason, resists containing aromatic compounds have been widely used. Much kind of resists contains novolac resin or polyhydroxystyrene, which are soluble to alkalis, were developed as a primary component.
In the mean time, with the recent increase in the density of integrated circuits, microprocessing technology today has been achieved to an order of subhalfmicron, and will be even required to smaller scale in the future. To meet this requirement, increasingly shorter wavelengths are used for photolithographic light sources, such as an ArF excimer laser beam with a wavelength of 193 nm and a fifth-harmonic YAG laser with a wavelength of 218 nm, which are experimentally applied to fine pattern forming. Copolymer such as polyacrylic acids combined with alicyclic compounds or the copolymer of norbornene and maleic anhydride were attempted to apply for resists for use at these short wavelengths, since phenol derivatives having a benzene ring as listed above are unsuitable for their poor transparency.
On the other hand, even finer patterning at 0.05 .mu.m or less is required for the experimental production of microwave semiconductor elements and quantum effect devices. However, resolution cannot be made significantly higher using polymerbased resists as listed above because of their shortcomings such as edge roughness due to large molecular sizes, as reported by Yoshimura, et al. (J. Photopolym. Sci. Technol., 10, 629 (1997)).
In an attempt to improve the resolution, an EB resist using a derivative of a cyclic phenol such as calixarene, which has a high heat resistance and a low molecular weight, has been reported (J. Photopolym. Sci. Technol., 10, 641 (1997)). However, calixarene does not easily dissolve in organic and water-base solvents because of its molecular structure and, furthermore, requires the use of an organic developer, which may be incompatible with the recent concern for environment.
An example of cyclic phenol derivative soluble to alkali solutions is the negative resist proposed by Nakamura, et al. (Chem. Lett. 1997 (3), 265), which uses cyclic resorcinol and contains methylol as a cross-linking agent. However, preparation of a tetramer or smaller polymer of resorcinol is difficult, and improvement of resolution is restricted.
While a resist which is developable with a water-base developer is desired, considering the concern for environment as mentioned above, the common development method with an alkali solution also involves cumbersome procedures such as the disposal of the alkaline developer. To reduce environment impact, it is preferred that the pH of the developer be lower than that of the existing ones. Currently available resists developable with a developer which has a pH of 11 or less, include polyvinyl alcohol, polyvinyl acetate or their copolymers with an acid anhydride. However, these resists have a disadvantage of high swelling property, which impairs the resolution in fine patterning.
For these reasons, it has been awaited to see a high-resolution resist composition which is soluble to a solvent for easy resist preparation and developable with an alkaline developer or a water-base developer of pH 11 or less, as well as a process for forming a resist pattern of a higher resolution. In consideration of the above, the objective of the present invention is to provide a high-resolution photosensitive composition developable by an alkaline or water-base developer and highly soluble to a solvent, and a pattern forming process using said photosensitive composition.